The aim of this interdisciplinary program is to determine the structure-function relationships and mechanisms of proteins in normal cardiovascular signaling and subject to abnormalities that cause disease. Major components (Projects 1, 2 and 3) address the mechanism and structure of small GTP-binding protein RhoA, its effector proteins and its mechanisms of regulation. RhoA regulates vascular smooth muscle contraction, cardiac hypertrophy and formation of stress fibers, and its downstream effector, Rho-kinase, was recently implicated in hypertension. The cellular mechanisms of RhoA and Rho-related proteins will be determined in Project 1, their atomic structures in Project 2, and their subcellular localization in Project 3 with proteins largely produced in Core B. The mechanisms of Ca2+-sensitization and the mechanisms of Ca}+-desensitization will be determined in Projects 1 and 3, and its subcellular localization of signaling proteins (sensitivity and de-sensitivity) in Project 3. The molecular structure of LPP, a newly discovered to be smooth muscle specific protein will be determined with combined X-ray crystallography and NMR spectroscopy (Project 2). The program will complete the development of a powerful structural method, energy filtered scanning transmission electron microscopy (STEM-EELS), that is designed to obtain compositional information at nanometer resolution about the cellular distribution and movement of calcium and other elements. This method will be used to quantitatively map calcium bound to a cardiac intercalated disc and vascular smooth muscle cell membranes, and accumulated in mitochondria and other organelles and will relate these findings to the normal functions and abnormal effects of calcium. The high level of biomedical significance of this is derived from the involvement of the smooth muscle regulatory proteins in asthma and high blood pressure, and from the importance of calcium in the development of ventricular fibrillation, the most common cause of sudden cardiac death.